Claims:WE CLAIM:
1. A variable valve lift system (100) for an internal combustion engine (12), comprising:
a camshaft (110) having a plurality of lobes (112), the plurality of lobes comprising at least one intake cam lobe and at least one exhaust cam lobe;
a rocker shaft (120);
at least one rear rocker member (130) mounted on the rocker shaft (120), the rear rocker member (130) rotatably engaged with the plurality of lobes (112) of the camshaft (110);
at least one forward rocker member (140) engaged with the rear rocker member (130), the forward rocker member (140) configured for lifting at least one valve (150) of the internal combustion engine (12);
a variable valve lift lever (160) pivotally mounted on the rear rocker member (130), the variable valve lift lever (160) having a protrusion (164) disposed in contact with the rear rocker member (130) and the forward rocker member (140); and
a selector pin assembly (170) having a selector pin (172) configured to engage or disengage with the variable valve lift lever (160) causing the variable valve lift lever (160) to pivot on the rear rocker member (130) thereby varying a rocker ratio.
2. The variable valve lift system (100) as claimed in claim 1, wherein the selector pin (172) of the selector pin assembly (170) is configured to engage or disengage with the variable valve lift lever (160), based on an RPM of the internal combustion engine (12).

3. The variable valve lift system (100) as claimed in claim 1, wherein the variable valve lift lever (160) comprises an indented extension (162), such that the selector pin (172) is configured to engage or disengage with the variable valve lift lever (160) at the indented extension (162) of the variable valve lift lever (160).

4. The variable valve lift system (100) as claimed in claim 1, wherein the protrusion (164) of the variable valve lift lever (160) comprises a cylindrical projection disposed in contact with the rear rocker member (130) and the forward rocker member (140).

5. The variable valve lift system (100) as claimed in claim 1, wherein the selector pin (172) is configured to be disengaged with the variable valve lift lever (160) up to a first predetermined RPM (R1) of the internal combustion engine (12).

6. The variable valve lift system (100) as claimed in claims 2 and 3, wherein the selector pin (172) is configured to move into a first engaged position with the indented extension (162) of the variable valve lift lever (160) at a second predetermined RPM (R2) of the internal combustion engine (12), causing the variable valve lift lever (160) to pivot in the rear rocker member (130) thereby increasing the rocker ratio for increasing a valve lift.

7. The variable valve lift system (100) as claimed in claim 5 and 6, wherein the disengaged position of the selector pin (172) is farther from the camshaft (110) than the first engaged position of the selector pin (172).

8. The variable valve lift system (100) as claimed in claim 5 and 6, wherein the second predetermined RPM (R2) of the internal combustion engine (12) is greater than the first predetermined RPM (R1) of the internal combustion engine (12).

9. The variable valve lift system (100) as claimed in claim 2 and 3, wherein the selector pin (172) is configured to move into a second engaged position with the indented extension (162) of the variable valve lift lever (160) at a third predetermined RPM (R3) of the internal combustion engine (12), causing the variable valve lift lever (160) to further pivot in the rear rocker member (130), thereby further increasing the rocker ratio for further increasing the valve lift.

10. The variable valve lift system (100) as claimed in claim 6 or 9, the first engaged position of the selector pin (172) is farther from the camshaft (110) than the second engaged position of the selector pin (172).

11. The variable valve lift system (100) as claimed in claim 6 or 9, wherein the third predetermined RPM (R3) of the internal combustion engine (12) is greater than the second predetermined RPM (R2) of the internal combustion engine (12).

12. The variable valve lift system (100) as claimed in claim 1, wherein the selector pin assembly (170) comprises a driving means for moving the selector pin (172).

13. The variable valve lift system (100) as claimed in claim 12, wherein the driving means for moving the selector pin (172) comprises a stepper motor or a servo motor (174) coupled with a helical shaft (176).

14. An engine assembly (200) for a variable valve lift system (100), comprising;
a camshaft (110) having a plurality of lobes (112), the plurality of lobes (112) comprising at least one intake cam lobe and at least one exhaust cam lobe;
a rocker shaft (120);
at least one rear rocker member (130) mounted on the rocker shaft (120), the rear rocker member (130) rotatably engaged with the plurality of lobes (112) of the camshaft (110);
a variable valve lift lever (160) pivotally mounted on the rear rocker member (130), the variable valve lift lever (160) having a protrusion (164) disposed in contact with the rear rocker member (130) and the forward rocker member (140);
at least one forward rocker member (140) engaged with the rear rocker member (130) via the protrusion (164), the forward rocker member (140) having a cavity (142) opening towards the protrusion (164), thereby forming an oil path and allowing oil passing from the forward rocker member (140) to fall on to the protrusion (164) through the cavity (142).

15. The variable valve lift system (100) as claimed in claim 14, wherein the cavity (142) on the forward rocker member (140) has an oval shape.
16. The engine assembly (200) as claimed in claim 14, wherein the protrusion (164) of the variable valve lift lever (160) comprises a cylindrical projection.

, Description:FIELD OF THE INVENTION
[001] The present invention relates to a variable valve lift system for an internal combustion engine.

BACKGROUND OF THE INVENTION
[002] In conventional motor vehicles, a fixed timing or lift mechanism for operation of intake and exhaust valves in an internal combustion engine allows for optimum performance only at a narrow band of engine speed.
[003] In conventional four-stroke internal combustion engines, a camshaft is provided to govern opening and closing of intake and exhaust valves of the engine. Generally, the camshaft has a profile or lobes, which dictate value of lift of the exhaust valves. For a given engine architecture, a higher value of lift results in a better power output at higher engine RPM. However, the so obtained higher value of lift will not provide an optimum power output when the engine RPM is lower. Contrastingly, a lower value of lift results in a good power output at lower engine RPM but will hamper performance at higher speeds. Thus, there is a trade-off between the value of lift of the exhaust valves and the power output of the engine.
[004] The existing valve lift systems that achieve variable lift, use camshaft with multiple cam lobes for operating a single valve. In such systems, the value of the lift changes in two or three steps depending upon number of cam lobes. Therefore, as compared to a fixed valve lift system, these systems are capable of providing one or two additional values of lift changes. Thus, the level of optimization of the power output of the engine across various engine speeds is not very different from the conventional non-variable valve lift systems.
[005] Other known systems that achieve variable valve lift do so by using a set of multiple linkages. In such systems, due to added engine components, the size of the engine is increased which leads to challenges in packing of the engine, especially in saddle-type vehicle. Further, the reliability of such systems decreases over time as the system components start to wear out. Also known are systems that achieve variable valve lift by use of electro-mechanical or electro-hydraulic systems, which not only increase engine complexity, but also increase engine size.
[006] The existing systems that achieve variable valve lift are generally suitable for implementation only in engines with Dual Over Head Camshaft (DOHC) architecture and cannot be implemented in engine with Single Over Head Camshaft (SOHC) architecture, which is the engine architecture primarily applied in saddle-type vehicle.
[007] Thus, there is a need in the art for a variable valve lift system for an internal combustion engine which addresses at least the aforementioned problems.

SUMMARY OF THE INVENTION
[008] In one aspect, the present invention is directed at a variable valve lift system for an internal combustion engine. The variable valve lift system has a camshaft with a plurality of lobes. The plurality of lobes have at least one intake cam lobe and at least one exhaust cam lobe, and a rocker shaft. At least one rear rocker member is mounted on the rocker shaft and is rotatably engaged with the plurality of lobes of the camshaft. At least one forward rocker member is engaged with the rear rocker member and is configured for lifting at least one valve of the internal combustion engine. A variable valve lift lever is pivotally mounted on the rear rocker member. A protrusion on the variable valve lift lever is disposed in contact with the rear rocker member and the forward rocker member. A selector pin assembly having a selector pin is configured to engage or disengage with the variable valve lift lever for causing the variable valve lift lever to pivot on the rear rocker member, thereby varying a rocker ratio.
[009] In an embodiment of the invention, the selector pin of the selector pin assembly is configured to engage or disengage with the variable valve lift lever, based on an RPM of the internal combustion engine.
[010] In another embodiment of the invention, the variable valve lift lever has an indented extension such that the selector pin is configured to engage or disengage with the variable valve lift lever at the indented extension of the variable valve lift lever.
[011] In another embodiment of the invention, the protrusion of the variable valve lift lever has a cylindrical projection disposed in contact with the rear rocker member and the forward rocker member.
[012] In another embodiment of the invention, the selector pin is configured to be disengaged with the variable valve lift lever up to a first predetermined RPM of the internal combustion engine.
[013] In another embodiment of the invention, the selector pin is configured to move into a first engaged position with the indented extension of the variable valve lift lever at a second predetermined RPM (R2) of the internal combustion engine. This causes the variable valve lift lever to pivot in the rear rocker member thereby increasing the rocker ratio for increasing a valve lift. Herein, the disengaged position of the selector pin is farther from the camshaft than the first engaged position of the selector pin. Further, the second predetermined RPM of the internal combustion engine is greater than the first predetermined RPM of the internal combustion engine.
[014] In another embodiment of the invention, the selector pin is configured to move into a second engaged position with the indented extension of the variable valve lift lever at a third predetermined RPM of the internal combustion engine. This causes the variable valve lift lever to further pivot in the rear rocker member, thereby further increasing the rocker ratio for further increasing the valve lift. Herein, the first engaged position of the selector pin is farther from the camshaft than the second engaged position of the selector pin. Further, the third predetermined RPM of the internal combustion engine is greater than the second predetermined RPM of the internal combustion engine.
[015] In another embodiment of the invention, the selector pin assembly has a driving means for moving the selector pin.
[016] In another embodiment of the invention, the driving means for moving the selector pin has a stepper motor or a servo motor coupled with a helical shaft.
[017] In another aspect, the present invention relates to an engine assembly for a variable valve lift system. Herein, a camshaft has a plurality of lobes, and the plurality of lobes have at least one intake cam lobe and at least one exhaust cam lobe. At least one rear rocker member is mounted on a rocker shaft and is rotatably engaged with the plurality of lobes of the camshaft. A variable valve lift lever is pivotally mounted on the rear rocker member, and has a protrusion disposed in contact with the rear rocker member and the forward rocker member. Further, at least one forward rocker member is engaged with the rear rocker member via the protrusion. Herein, the forward rocker member has a cavity that opens towards the protrusion, thereby forms an oil path for allowing oil passing from the forward rocker member to fall on to the protrusion through the cavity.
[018] In an embodiment of the invention, the cavity on the forward rocker member has an oval shape.
[019] In another embodiment of the invention, wherein the protrusion of the variable valve lift lever has a cylindrical projection.

BRIEF DESCRIPTION OF THE DRAWINGS
[020] Reference will be made to embodiments of the invention, examples of which may be illustrated in accompanying figures. These figures are intended to be illustrative, not limiting. Although the invention is generally described in context of these embodiments, it should be understood that it is not intended to limit the scope of the invention to these particular embodiments.
Figure 1 illustrates a right-side view of an exemplary motor vehicle, in accordance with an embodiment of the invention.
Figure 2 illustrates a sectional view of a variable valve lift system implemented in an engine assembly, in accordance with an embodiment of the invention.
Figure 3 illustrates a perspective view of a disengaged position of a selector pin in the variable valve lift system, in accordance with an embodiment of the invention.
Figure 4 illustrates a perspective view of an engaged position of the selector pin in the variable valve lift system, in accordance with an embodiment of the invention.
Figure 5A and 5B illustrate a rear rocker member of the variable valve lift system, in accordance with an embodiment of the invention.
Figure 6A, 6B and 6C illustrate a forward rocker member of the variable valve lift system, in accordance with an embodiment of the invention.
Figure 7A and 7B illustrates a variable valve lift lever of the variable valve lift system, in accordance with an embodiment of the invention.
Figure 8A and 8B illustrate a selector pin assembly of the variable valve lift system, in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION
[021] The present invention relates to an internal combustion engine. More particularly, the present invention relates to a variable valve lift system for an internal combustion engine.
[022] Figure 1 illustrates an exemplary motor vehicle 10, in accordance with an embodiment of the invention. The motor vehicle 10 has an internal combustion engine 12 that is vertically disposed. Preferably, the internal combustion engine 12 is a single-cylinder type internal combustion engine. The motor vehicle 10 has a front wheel 14, a rear wheel 16, a frame member, a seat assembly 18 and a fuel tank 20. The frame member includes a head pipe 22, a main tube 24, a down tube (not shown), and seat rails (not shown). The head pipe 22 supports a steering shaft (not shown) and two telescopic front suspensions 26 (only one shown) attached to the steering shaft through a lower bracket (not shown). The two telescopic front suspensions 26 support the front wheel 14. The upper portion of the front wheel 14 is covered by a front fender 28 mounted to the lower portion of the telescopic front suspension 26 at the end of the steering shaft. A handlebar 30 is fixed to upper bracket not shown and can rotate to both sides. A head light 32, a visor guard (not shown) and instrument cluster (not shown) is arranged on an upper portion of the head pipe 22. The frame member comprises a down tube (not shown) that may be located in front of the internal combustion engine 12 and extends slantingly downward from head pipe 22. The main tube 24 of the frame member is located above the internal combustion engine 12 and extends rearward from head pipe 22. The internal combustion engine 12 is mounted at the front to the down tube and a rear of the internal combustion engine 12 is mounted at the rear portion of the main tube 24. In an embodiment, the internal combustion engine 12 is mounted vertically, with a cylinder block extending vertically above a crankcase. In an alternative embodiment, the internal combustion engine 12 is mounted horizontally (not shown) with the cylinder block extending horizontally forwardly from the crankcase. In an embodiment, the cylinder block is disposed rearwardly of the down tube.
[023] The fuel tank 20 is mounted on the horizontal portion of the main tube 24. Seat rails are joined to main tube 24 and extend rearward to support a seat assembly 18. A rear swing arm 34 is connected to the frame member to swing vertically, and the rear wheel 16 is connected to rear end of the rear swing arm 34. Generally, the rear swing arm 34 is supported by a mono rear suspension 36 (as illustrated in the present embodiment) or through two suspensions on either side of the motor vehicle 10. A taillight unit 33 is disposed at the end of the motor vehicle 10 and at the rear of the seat assembly 18. A grab rail 35 is also provided on the rear of the seat rails. The rear wheel 16 arranged below seat 18 rotates by the driving force of the internal combustion engine 12 transmitted through a chain drive (not shown) from the internal combustion engine 12. A rear fender 38 is disposed above the rear wheel 16.
[024] Further, an exhaust pipe 40 of the vehicle extends vertically downward from the Internal combustion engine 12 up to a point and then extends below the Internal combustion engine 12, longitudinally along the vehicle length before terminating in a muffler 42. The muffler 42 is typically disposed adjoining the rear wheel 16.
[025] As illustrated in Figure 2, the variable valve lift system 110 has a camshaft 110 with a plurality of lobes 112. Herein, the plurality of lobes 112 have at least one intake lobe that operates an intake valve during an intake stroke of the internal combustion engine 12, and at least one exhaust lobe that operates an exhaust valve during an exhaust stroke of the internal combustion engine 12. The variable valve lift system 100 further has a rocker shaft 120, on which at least one rear rocker member 130 is mounted. The rear rocker member 130 is mounted on the rocker shaft 120 in manner that the rear rocker member 130 is rotatably engaged with the lobes 112 on the camshaft 110 via a notch 134 (as also shown in Figures 5A and 5B) on the rear rocker member 130. In that, as the camshaft 110 rotates, the lobes 112 come in contact with the rear rocker member 130, causing the rear rocker member 130 to pivot on the rocker shaft 120.
[026] Further, the variable valve lift system 100 has at least one forward rocker member 140 mounted on the rocker shaft 120 at a first groove 146 (as shown in Figures 6A and 6B) and is engaged with the rear rocker member 130. The forward rocker member 140 is further connected to at least one valve 150 at a second groove 148 (shown in Figure 6A) provided on the forward rocker member 140. The forward rocker member 140 is configured for lifting the valve 150. As further illustrated in Figure 2, the variable valve lift system 100 further has a variable valve lift lever 160 that is pivotally mounted on the rear rocker member 130. In an embodiment of the invention, the variable valve lift lever 160 is pivotally mounted on a slot 132 (as also shown in Figures 5A and 5B) on the rear rocker member 130. The variable valve lift lever 160 has a protrusion 164 thereon, which is disposed in contact with the rear rocker member 130 and the forward rocker member 140, and is configured to move between the forward rocker member 140 and the rear rocker member 130.
[027] In operation, rotation of the camshaft 110 is transmitted to the rear rocker member 130 through the lobes 112. The pivot movement of the rear rocker member 130 on the rocker shaft 120 is transmitted to the forward rocker member 140 through the protrusion 164 on the variable valve lift lever 160, and thereafter the forward rocker member 140 lifts the valve 150.
[028] The variable valve system 100 further has a selector pin assembly 170 having a selector pin 172 that is configured to engage or disengage with the variable valve lift lever 160. In conditions where the selector pin 172 is engaged with the variable valve lift lever 160, the engagement causes the variable valve lift lever 160 to pivot on the rear rocker member 130, thereby causing the protrusion 164 of the variable valve lift lever 160 to move between the rear rocker member 130 and the forward rocker member 140 which varies a rocker ratio. For the purpose of the present invention, rocker ratio is defined as the ratio of the distance of the mounting location of the valve 150 on the forward rocker member 140 from the rocker shaft 120 (L1) to the distance of the notch 134 on the rear rocker member 130 from the rocker shaft 120 (L2).
[029] There is a direct relationship between the rocker ratio and valve lift, wherein value of valve lift is directly proportional to the rocker ratio (L1/L2). In the present invention, as the variable valve lift lever 160 pivots on the rear rocker member 130, the protrusion 164 of the variable valve lift lever 160 moves upwards between the rear rocker member 130 and the forward rocker member 140. This effectively increases the value of L1 and thereby increases the rocker ratio. Herein, greater the degree of pivot of the variable valve lift lever 160, greater is the rocker ratio and hence, greater the value of achieved valve lift.
[030] In an embodiment of the invention, the selector pin 172 of the selector pin assembly 170 is configured to engage or disengage with the variable valve lift lever 160, based on an RPM of the internal combustion engine 12.
[031] Figure 3 illustrates a perspective view of a disengaged position of the selector pin 172 in the variable valve lift system 100, in accordance with an embodiment of the invention. As illustrated in Figure 3, and further illustrated in Figure 7A and Figure 7B, the variable valve lift lever 160 has an indented extension 162. The selector pin 172 is configured to engage or disengage with the variable valve lift lever 160 at the indented extension 162. Further, the protrusion 164 of the variable valve lift lever 160 has a cylindrical projection disposed in contact with the rear rocker member 130 and the forward rocker member 140.
[032] As illustrated in Figure 3, the selector pin 172 is configured to be disengaged with the variable valve lift lever 160 up to a first predetermined RPM (R1) of the internal combustion engine 12. Herein, the variable valve lift lever 160 will not pivot on the rear rocker member 130. Hence there is no movement of the protrusion 164 between the rear rocker member 130 and the forward rocker member 140. Therefore the movement of the rear rocker member 130 is transmitted to the forward rocker member 140 at a low rocker ratio.
[033] As illustrated in Figure 4, the selector pin 172 is configured to move into a first engaged position with the indented extension 162 of the variable valve lift lever 160 at a second predetermined RPM (R2) of the internal combustion engine 12. Herein, the second predetermined RPM (R2) is greater than the first predetermined RPM (R1). The pivot movement of the selector pin 172 in to the first engaged position causes the variable valve lift lever 160 to pivot in the rear rocker member 130. This results in upward movement of the protrusion 164 between the rear rocker member 130 and the forward rocker member 140, thereby an increase in the rocker ratio for increasing valve lift. As illustrated in Figure 4 and referenced in Figure 3, the disengaged position of the selector pin 172 is farther from the camshaft 110 than the first engaged position of the selector pin 172. In this regard the selector pin 172 is configured to move towards the camshaft 110 axis, as the selector pin 172 moves from the disengaged position to the first engaged position. As the second predetermined RPM (R2) is greater than the first predetermined RPM (R1), greater valve lift is required corresponding to higher RPM. This is generated by the variable valve lift system 100 of the present invention.
[034] As the RPM of the internal combustion engine 12 further increases, there arises a need to further increase valve lift. To achieve this, the selector pin 172 is configured to move into a second engaged position with the indented extension 162 of the variable valve lift lever 160 at a third predetermined RPM (R3) of the internal combustion engine 12. This causes the variable valve lift lever 160 to further pivot in the rear rocker member 130, thereby resulting in further upward movement of the protrusion 164 between the rear rocker member 130 and the forward rocker member 140. This increases the rocker ratio for further increasing the valve lift. Herein, the third predetermined RPM (R3) is greater than the second predetermined RPM (R2) . Further, the first engaged position of the selector pin 172 is farther from the camshaft 110 than the second engaged position of the selector pin 172.In this regard, the selector pin 172 is configured to move towards the the camshaft 110 axis with increasing RPM, thereby increasing the valve lift with increasing RPM of the internal combustion engine 12.
[035] As illustrated in Figure 8A and 8B, the selector pin assembly 170 has a driving means for moving the selector pin 172. Herein, the driving means for moving the selector pin 172 comprises a stepper motor or a servo motor 174 coupled with a helical shaft 176. The selector pin 172 is attached at one end of the helical shaft 176 while the other end of the helical shaft 176 is operable by the stepper motor or the servo motor 174 for moving the selector pin 172 forward and backward, thereby moving the selector pin 172 to engage or disengage with the variable valve lift lever 160. In an embodiment of the invention, the stepper motor or the servo motor 174 is configured to be controlled by a controller that gauges the RPM of the internal combustion engine 12 and drives the stepper motor or the servo motor 174 accordingly to move the selector pin 172.
[036] As is understood from the foregoing disclosure, under conditions wherein the selector pin 172 is disengaged with the variable valve lift lever 160, there is no relative motion between the protrusion 164 on the variable valve lift lever 160 and the forward rocker member 140. Conversely, under conditions wherein the selector pin 172 is engaged with the variable valve lift lever 160, there is a relative motion between the protrusion 164 on the variable valve lift lever 160 and the forward rocker member 140. This relative motion leads to a substantially high friction between the protrusion 164 and the forward rocker member 140. The motion of the forward rocker member 140 may also lead to obstruction in the oil passageway 144 (shown in Figure 6C) provided on the forward rocker member 140.
[037] To address this issue, in one aspect, the present invention provides an engine assembly 200 for the internal combustion engine 12, in which the variable valve lift system 100 has been implemented, as referenced in Figure 2. Herein, the forward rocker member 140 has a cavity 142 (shown in Figure 6C) provided thereon. The cavity 142 on the forward rocker member 140 opens towards the protrusion 164. The cavity 142 is configured to receive a part of the oil travelling in the forward rocker member 140 and provide an exit for the oil. The configuration of the variable valve lift system 100 in the engine assembly 200, allows for oil exiting the cavity 142 on the forward rocker member 140 to fall on to the protrusion 164 assisted by gravity, thereby lubricating a surface of the forward rocker member 140 and the protrusion 164 where the relative motion occurs.
[038] Further, in an embodiment of the invention, the cavity 142 on the forward rocker member 140 has an oval shape, and the protrusion 164 on the variable valve lift lever 160 has a cylindrical projection. The oval shape of the cavity 142 ensures that even when the cylindrical projection is in a position wherein the cylindrical projection is in front of the cavity 142, the cylindrical projection does not fully shut the cavity 142, thereby allowing the oil to pass through the cavity 142 under all operating conditions, thereby providing adequate lubrication.
[039] Advantageously, the present invention discloses a variable valve lift system that provides an increase in the valve lift based on the RPM of the internal combustion engine. The variable valve lift system of the present invention achieves non-discrete values of valve lift, thereby achieving a higher level of valve lift optimisation as compared to conventional systems.
[040] Further, the variable valve lift system of the present invention provides a reliable system without any electro-mechanical or electro-hydraulic systems, and hence can be implemented in a compact engine architecture. Also, the lubrication provided to the system through the cavity on the forward rocker member ensures that the components of the variable valve lift system are adequately lubricated in all running conditions, bringing down the long term wear and tear caused to the components in operation.
[041] Furthermore, the variable valve lift system of the present invention is capable of being implemented in an engine with Single Over Head Camshaft (SOHC) architecture, and hence suitable for application in saddle-type vehicles.
[042] While the present invention has been described with respect to certain embodiments, it will be apparent to those skilled in the art that various changes and modification may be made without departing from the scope of the invention as defined in the following claims.